The bedrock in SW Wisconsin is a group called Sinippee or similar name. The upper part formation is called Platteville Dolomite. Many problems with the rock there.
This map shows that same rock is under the Green Bay area. In my experience in souith-west Wisconsin we have drilled a bunch of quarry holes at the bottom of significant foundations (such as water towers) to look for weak stuff below. Sometimes, under pretty good rock there are cavities and crevices filled with soft clay, sometimes the end product of weathering. A few caves have been found. Apparently the steel piles were founded on bedrock, but it is unlikely any test hole was drilled at that pier, at least into rock any distance. Apparently rock is 100 feet down.
I'll betcha many a core drill hole is coming up, up and down the alignment.
Now let's cogitate about what to do with the questionable areas? Flush out the clay and grout? Jack the pile cap back up and test each pile? Gosh what a discussion can be had on this fix?
If one went bad, the others must be checked as well. Considering the cost of a replacement structure where the same thing would have to be done, they might as well do exploratory drilling at each and every existing pier.
Then comes the fun stuff. Questions:
Could the pier be raised hydraulically by pressurized grouting? Probably not...
Stabilize the pier for gravity forces, jack up the bridge to the original level, and add a new metal structure to the top of the pier?
"If one went bad, the others must be checked as well. Considering the cost of a replacement structure where the same thing would have to be done, they might as well do exploratory drilling at each and every existing pier."
Jed: Soft limestone may be to blame, soft like the Packers' defense thus far, which results in a bend but don't break philosophy. They need to get Raaji and Mathews to lift up the pile via deadlift while pressure grouting under the pile.
msquared: They may be able to use pressure grouting to get some lift, it is what we use to remediate sinkhole activity in Florida and does a good job of sealing off cavities in the limestone and filling and compacting any loose sandy soils. At a minimum, I would not be surprised if they did this to at least fill any cavities or loose zones that may have caused the failure. Lift would depend on the grout pressure they could develop versus the resistance of the pile (bridge load, skin friction, etc). Grout may just blow out laterally or vertically prior to developing enough pressure to get any appreciable uplift. These are my guesses, I don't have specific grouting under piles knowledge but I think in theory it could work. They may just have to grout to seal and stabilize the bottom of the pile and then fix the structure on the top side...
Hokie:
My boss is a PhD geologist and said that the type of dolomite, shale and limestone in that part of Wisconsin is VERY old and usually very weathered, hard and dense, and is not normally subject to dissolution and weakening mechanisms the way it occurs with Florida's limestone (we are a Florida based geology and engineering company). BUT- it is possible there was a cavity or soft zone in the rock, and they will obviously have to confirm with testing.
“This does not indicate the rest of the bridge is in danger of collapse,” he said. “These foundations, these piles, have huge safety factors on them so if one pile fails there are 39 others to support the bridge.”
So I take it that each of the 51 or so piers has 40 pile supporting it? With a failure of this magnitude, across the whole pier line, it appears to me that all 40 pile collapsed within a few hours, not just one. Where is this guy coming from?
Apparently the bedrock is not the issue now. Peat soil? Ice removal salting dumped down the piers? How do you now fix things? A report says the fix is $50 million. How?
According to the article posted above, the culprit may be foundry sand.
I wonder if all of this will make us rethink how we design pile supported foundations. The corrosion and buckling of 40 steel piles all at once is something I never dreamed could happen. Probably corrosion had already compromised many of the piles, and collapse occurred when the last few remaining piles corroded.
As of today (Saturday the 5th) a couple of recent TV videos are on line. Looks like a soil scientist is involved as to chemistry. I hope they also look at roadway de-icing that probably results in that salty water at each pier near a scupper outlet.
As to ground conditions and corrosion, highway design engineers (not the bridge section designers) know about that problem and pave the inverts of corrugated culverts in peaty areas. In my experience at the WiDOT years ago, there were obvious waterproof walls between various sections, such as maintenance, bridge, construction, etc. Little kingdoms develop and it is difficult to get any changes or to have any one even listen. For instance, what bridge design manual covers the pH of soil as something to look at? Who ever from construction division goes back and checks for corrosion . Maintenance guys struggle with what is dealt them in many ways from bridges to roadways. Farming design work out to consultants can be even more difficult for down the road checking of performance getting back to designers.
